Molding articles of manufacture through the use of various molding techniques such as die casting and sand casting are well known. These techniques generally entail heating a metal material to a temperature that equals or exceeds its melting point, allowing the metal material to melt into a liquid material, and then pouring the liquid material into a metal or sand mold that has a desired shape to form an article of manufacture. Once the liquid material is in the mold, it is allowed to cool and solidify. Once solidified, the metal material is removed from the mold.
It is common practice to position inserts referred to as cores in sand casting into the mold during the molding process to form cavities in the metal material as it solidifies. For example, when forming an engine block for an automobile engine, it is common to position inserts into the mold at locations where the engine's cylinders will be located. This obviates the need to bore material out of an otherwise solid engine block.
When certain metal alloys are molded in the manner described above, it is sometimes desirable to accelerate the cooling process. For example, when forming an engine block from an aluminum alloy, it may be desirable to cool the molten aluminum alloy in the immediate vicinity of the cylinder cavities as quickly as possible. This accelerated cooling will yield cylinder bores having wear properties that are superior to cylinder bores of aluminum alloy engine blocks that are cooled more slowly.
To accelerate the cooling of the metal alloy in the vicinity of a cavity, the insert that is used to form the cavity is conventionally made of metal. Because of the ability of metal to conduct heat, the presence of the metal insert in the molten metal material draws heat out of the molten material causing it to cool more quickly. Such a metal insert is commonly referred to as a “chill”. As the molten metal material cools and solidifies, it contracts around the chill, making it difficult to remove the chill from the solid metal material. Frequently, a high degree of force is required to extract the chill from the solidified metal material. As a result, after repeated use, the chill can become scored or otherwise damaged and may need to be replaced. Also scoring of the bores or block distortion may result from this force.
In the die casting process, the metal tooling acts as the chill. However because of the contraction of the cast metal onto the die tooling, the block becomes difficult to remove from the die, resulting in tool wear, block distortion and damage to the casting bore surface. Excess draft is added to the tool to help removal but this generally requires additional machining after the casting has hardened to compensate for the draft. This, in turn, adds costs and may adversely affect the properties of the final bore surface structure.